Stabilized panel production



March 29, 1966 w. D. VOELKER STABILIZED PANEL PRODUCTION Filed Feb. 8, 1962 INVENTO Waffer l/aaer BYMQM ATTORN EY United States Patent O 3,243,492 STABILZED PANEL PRDUCTHUN Waiter D. Voelker, Phiiadelphiahlla., assignor, by mesne assignments, to Allied Chemical Corporation, New York, NY., a corporation of New York Filed Feb. 8, 1962, Ser. No. 171,849 1 Claim. (Cl. 264-646) This invention relates to the manufacture of. polyurethane foam panels and particularly to the stabillzation of panels whereby they may retain predetermined dimensions and possess greater resistance to saggmg and creeping than has been true of some poljmrethane foam panels previously produced.

Heretoifore there have been proposals for the production of rigid panels of polyurethane foam (for use as ceiling tile, wall insulation, and other applicatlon in which the superior insulating characteristics of polyurethane foam are advantageous. In some of the applications, the panels have been positioned in structures so that they retain ltheir original dimensions notwithstanding dlfferences in the humidity and/ or other conditions around the surfaces of the panel. When employed as tile for suspended ceilings, the insulation panels must not undergo any sagging or warping or creeping, inasmuch as even'small openings in the suspended ceilings significantly impair the insulating eiiciency of the suspended ceiling.

During the development of the present invention is was discovered Vthat the rigid polyurethane ffoam leaving the end of the production line for panel manufacture was somewhat sensitive to water, steam and moisture, whereby panels subjected to atmospheres having a different humidity tended to warp, sag and/ or creep during a prolonged period of time.

In accordance with the present invention, rigid panels of polyurethane foam are subjected to ya high humidity zone at an elevated temperature to bring about a stabilization of the dimensions of the panels.

The nature of the invention is further lclaried by reterence to the accompanying drawing which is a schematic view of a panel production line utilizing the steam stabilization step of the present invention.

Referring now to the drawings, there is shown schematically a panel production machine in which a strip of sheet material 111 passes successively through a coating zone 12, metering zone 13, curing zone 14, drying zone 15, and product removal zone 16. In the product removal zone 16, panels 17, characterized primarily by a major volume of polyurethane foam, are removed from the panel production machine 10.

Particular attention is directed to a steam oven 18 through which the panels 17 pass while being heated to an elevated temperature and being subjected to high humidity. The panels may be stacked upon wagons 19 which are pulled through the steam oven '18 at a forward speed significantly less than the forward speed of the advancing sheet 1-1 of the panel production machine 10. The steam oven is provided with a tunnel through Iwhich the panels move while being heated and humidied. Suitable thermostats 20 and humidistats 21 maintain the 3,243,492 Patented Mar. 29, 1966 ICC predetermined temperature and humidity throughout the various stages of Ithe movement of the wagons 19 through the steam oven 18. A furnace 22 provides flue gas which is blown into the steam oven together with additional steam :formed lat water spray jets 23. A `fan 24 may recirculate a portion of the gases in the steam oven and a portion may be withdrawn through a chimney 25. `In the loperation of the steam oven in accordance with the present invention, it is necessary to maintain a temperature within the range from 60 to 135 degrees C.; a water vapor pressure within the range from about 145 yto about 760 millimeters of mercury pressure; and a relative humidity within the range from 95 percent to about 30 percent. Such conditions must lbe maintained around the panels for a time period within the range from 10 to 300 minutes, and ordinarily will be maintained throughout about percent of the path of wagons through the steam furnace. The wagons 119 leaving the steam oven advance to an Aunloading zone from which the panels 17 may be removed for shipment to the user.

Various modifications are possible without departing from the scope 4of Ithe invention as set forth in the appended claim.

What is claimed is:

yIn a process for the production of a rigid polyurethane foam panel wherein a lcore of rigid polyurethane foam is bonded to at least one facing sheet the improvement which comprises introducing the said panel after curing of the said foam core into a stabilizing zone and maintaining the said panel in the said stabilizing zone for a period of from about 10 minutes to about 300 minutes; the temperature in the said stabilizing zone being in the range from about 60 C. to about 135 C. and the relative humidity in the said stabilizing zone being in the range yfrom about percent to about 30 percent, with the proviso that the pressure of Water vapor in the said stabilizing zone is from about to about 760 millimeters of mercury; whereby the said panel is stabilized against warping and dimensional change in use.

the Society of Plastic Engineers, Feb. 2, 1962, Recent Advances in Technology of Rigid Urethane yFoams, note especially pp. 6 and 7.

EARL M. BERGERT, Primary Examiner.

C. B. COSBY, Assistant Examiner. 

